1. Field of the Invention
The invention generally relates to an optical device and a backlight module, and more particularly, to a light guide plate and a side type backlight module.
2. Description of Related Art
In recent years, liquid crystal display (LCD) has been broadly applied in our daily life along with the rapid development of flat panel display techniques. LCD has gradually replaced the conventional cathode ray tube (CRT) due to its many advantages such as light weight, small volume, low power consumption, and small thickness.
An LCD has a liquid crystal panel and a backlight module, wherein the backlight module is disposed behind the liquid crystal panel to provide a surface light source for the liquid crystal panel. A backlight module may be categorized as a direct type backlight module or a side type backlight module according to the disposed positions of light emitting devices thereof. In a side type backlight module, a light guide plate is disposed for guiding the light beams emitted by light emitting devices disposed at one side of the light guide plate, so as to provide a surface light source to the liquid crystal panel. Besides, a backlight module may also be categorized as a light emitting diode (LED) backlight module or a cold cathode fluorescent lamp (CCFL) backlight module according to the type of light emitting devices adopted therein.
In a side type backlight module having a plurality of LEDs as its light emitting devices, the LEDs are disposed beside an incident surface in the light guide plate, and the LEDs are arranged on a straight line and are kept away from each other. The LEDs emit a plurality of light beams, wherein the light beams enter the light guide plate through the incident surface of the light guide plate. Because the LEDs have higher directivity (i.e., have a limited light emitting angle range), bright regions are formed in the light guide plate within the light emitting angle range and close to the LEDs, and dark regions are formed in the light guide plate outside of the light emitting angle range. The light guide plate may not be able to provide a uniform surface light source due to the existence of these bright and dark regions, and this is referred to as the “hot spot” phenomenon. Along with the constant increase of LED power in recent years, the number of LEDs disposed at one side of the incident surface in the light guide plate is reduced. However, since fewer LEDs are disposed, the space between every adjacent two LEDs is increased. As a result, the surface areas of the dark regions are increased, and accordingly the surface light source becomes even more uneven and the problem of hot spot is worsened.